Throat plate for chain stitch sewing machines



April 1 4, 1970 w. STROTHMANN THROAT PLATE FOR CHAIN STITCH SEWING MACHINES 7 Filed July 15, 1967 3 Sheets-Sheet 1 INVENTOR IY/LFR/ED swam MANN 0 f o-P4 5 April 14, 1970 w. STROTHMANN 3,505,965

THROAT PLATE FOR CHAIN STITCH SEWING MACHINES 5 Sheets-Sheet 2 Filed July 13, 1967 I NVENTO R ,4 r role/vi) A ril 14, 1970 w. STROTHMANN 3,505,965

THROAT PLATE FOR CHAIN STITCH SEWING MACHINES Filed July 13, 1967 3 Sheets-Sheet 5 INVENTOR W/Z FRIED ST/POIHM/MW Ma-mg United States Patent Int. Cl. Db is/oo, 21/00 U.S. Cl. 112260 4 Claims ABSTRACT OF THE DISCLOSURE An insert for a throat plate adapted for use in a twothread chain-stitch sewing machine provided with means for forming a scam in every feed direction of a workpiece. This insert is provided essentially with a discshaped part having a stitch hole for the passage of the needle, and a sectional part surrounding the stitch hole on a section of its circumference and overtopping the throat plate, thus forming a supporting surface for the workpiece to prevent a downward stripping of the workpiece when pierced by the needle, and providing freedom of movement about the hole for tightening the loose needle thread loops when forming a seam in the area of movement of the workpiece which is clamped between clamping plates of a pattern controlled sewing devcie, the lower clamping plate being in alignment with the supporting surface of the insert.

BACKGROUND OF THE INVENTION A primary object of the invention is to develop a twothread chain stitch sewing machine, provided with a thread carrying needle, a thread carrying looper and a workpiece press pad to make possible the forming of a seam in every feed direction.

It is a further object of the invention to replace the lock stitch sewing machines, which have been used heretofore, in automatic sewing installations for producing collars, cuffs or workpieces, with changing direction of the seam and which cause a frequent interruption of the working process because of the limited thread supply on the lower thread bobbin. The lock stitch sewing machines are to be replaced by two-thread chain stitch sewing machines in order to eifect a substantial increase of efiiciency of the sewing installation since the lower thread bobbins in these machines are not exchanged.

There are already known two-thread chain stitch sewing machines which sew in every direction desired. For this purpose a rotatable movement is imparted to the spreader above the thread carrying looper. During this movement the spreader moves ahead with the looper and catches the looper thread as well as the needle thread loop hanging on the looper, between the looper head and the stitch hole. During the back movement, the spreader advances ahead of the looper and bends the threads in such a manner as to form a thread triangle for receiving the needle. The corner points of said thread triangle are always fixed in the same position by the looper, the spreader, and the stitch hole, irrespective of the direction and length of the feeding.

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Since in chain stitch sewing machines, the loop of the needle thread is only tightened during the next entrance of the needle, the stitch hole of these sewing machines is developed as an oblong hole in the direction of the sewing. Such a stitch hole, however, allows the forming of a seam only in one or two feed directions, even if the sewing machine is provided with sewing attachments which enable sewing in all directions. In order to be able to sew with the two-thread chain stitch sewing machine according to the above mentioned patent, in all directions, it has been proposed to provide the upper surface of the throat plate with a hollow around the stitch hole. However, this hinders the proper sewing of thin material, as this material is drawn by the needle down to the, bottom of the stitch hole during sewing, thus preventing an even tightening of the threads.

In order to eliminate this deficiency there has been proposed a throat plate, having three or more slots formed therein extending radially from the needle hole. The needle threads could thus be laid down in one of these slots in every feed direction, so that a satisfactory tightening of the threads would be obtained when the stitch was straightened. Such an arrangement is disclosed in U.S. Patent 3,313,259 of Apr. 11, 1967.

It is conceivable that when the workpiece is fed in certain directions, the threads do not slip off from the rounded ends of thearm into the slots, thus resulting in false stitches. The throat plate according to U.S. Patent No. 3,313,259 is not suitable for automatic sewing devices, in which the workpiece is clamped into holding frames.

These holding frames consist of a lower and an upper clamp plate, hingeably connected with each other and conforming to the outline of the workpiece. Especially for preventing the distortion of thin workpieces, it is nec essary to form the seam as close to the clamp plates of the holding frames as possible. Since the workpiece no longer rests in the area of the stitch hole on the clamp parts of the holding frames, due to the thickness of the lower clamp plate, it has been proposed to provide the throat plate of lock stitch sewing machines with a substantially conic or cylindrical inset, provided with a stitch hole. The workpiece can rest on this inset in cooperation with a workpiece press pad. Such an arrangement i disclosed in British Patent No. 900,039.

SUMMARY According to the invention, the objects are accomplished by a throat plate inset arranged in the area of the stitch hole of said throat plate, said throat plate inset being disc-shaped and movable and provided with a stitch hole and with a member for supporting the workpieces. Said member for supporting the workpieces is formed as a hollow cylindrical section or as a frusto-conical section.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a top plan view of an automatic sewing device with a rotatable table provided with workpiece clamps and a swingably supported two-thread chain stitch sewing machine with the throat plate according to the invention;

FIG. 2 is a partial top plan view, according to FIG. 1, partly in section;

FIG. 3 shows a section according to line IIIIII of FIG. 1 on an enlarged scale;

FIG. 4 is a section according to line IVIV of FIG. 3 with a view on the fabric carrier arm and a workpiece clamp holder;

FIG. 5 shows an enlarged section according to line VV of FIG. 4;

FIG. 6 shows a section through a modified form of a throat plate inset;

FIG. 7 is a diagrammatic top plan view of the throat plate and the workpiece clamp holder with a workpiece, partly in section;

FIG. 8 illustrates another sewing position according to FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT Distributed equally about the circumference of a turning table 1, are clamped exchangeable workpiece and pattern holders 2 in which the workpiece 3 are clamped for guidance under the needle 4 of a two-thread chain stitch sewing machine 7, according to the shape of guide patterns 8. The sewing machine 7 is mounted on a carrier arm 5 which is connected with a link arm 6, pivoted on the frame of the machine 9.

A driven magnetic roller 10 which cooperates with the guide patterns 8 is positioned in the carrier arm 5. On an elongation of the magnetic roller driving shaft 11 there is pivoted a loose guide roller 12, which is guided in a U- shaped guide rail 13, secured to the frame of the machine 9 In the fabric carrier arm 14 of the two-thread chain stitch sewing machine 7, there is provided a throat plate 15 (FIG. 4) which has a throat plate insert 16. The insert is formed with a disc-shaped part 17, running flush with the throat plate 15. The disk-shaped part 17 of the insert 16 is provided with a stitch hole 18 for the passage of needle 4, which cooperates with a thread carrying looper 19 and with a spreader 20 (FIGS. 7 and 8), said thread spreader allowing the formation of a seam in every feed direction. The throat plate insert 16, which is swingably supported in the throat plate 15, is further formed with sectional part which surrounds the stitch hole 18 on a section of its circumference and surmounts the throat plate. This sectional part may be formed as a partial frusto-conical section 21 or a hollow cylindrical section 22 (FIG. 6).

The height for either of the sections corresponds with the height of the lower clamp-plate 23 of the workpiece and pattern holders 2, so that the overhanging part of the workpiece 3, clamped between the lower and upper clamp plates 24 by means of a presser spring 25, runs parallel with the surface of the throat plate insert 16, whereby the workpiece 3, is guided between the insert 16 and a workpiece press pad 26.

The frusto-conical section 21 respectively the hollow cylinder section 22 as bevels 27, which extends on the vertical side edges of the sections 21, 22 and which have increasing widths vertically from the edge of the stitch hole 18 to the top surface of the sectional parts 21, 22 for forming an enlarged supporting surface for the work piece 3, to prevent a downward stripping of the workpiece 3 when pierced by the needle 4. Furthermore, it is the purpose of the bevel 27 to provide as much free room as possible in the area of the stitch hole 18 for tightening the loose needle thread loops (FIGS. 7, 8) when forming the seam in a relatively large area of movement.

The operation of the two-thread chainstitch sewing machine provided with a throat plate insert according to the invention is as follows:

The driven magnetic roller 10 (FIGS. 1-3) abutting the patterns 8 drives the turntable 1 in direction of the arrow (FIG. 2). The sewing machine 7 which is in hinged connection with the frame 9 moves only in the direction to the axis of the turntable 1 during rotation of it, caused by the guidance of the loose guide roller 12 in the U- shaped guide rail 13. Thus, the sewing machine 7 is nearly in a position in relation to the workpiece holder as shown in FIGS. 1, 3 and 4. Caused by the position of the throat plate insert 16 with reference to the fabric carrier arm 14 (FIG. 4) and the constructions of the insert 16 with the bevels 27 extending on the vertical side edges of the sectional part 21 and having increasing widths vertically from the edge of the stitch hole 18 (FIG. 5) to the top surface of the sectional part 21 it is possible that on forming seams to be made on the three edges of a workpiece 3 during the movement of the turntable 1 there will always exist sufiicient free room in the area of the stitch hole 18 for tightening the loose needle thread loops, which is necessary when forming a double chainstitch seam.

Whatl claim is:

1. A two-thread chain-stitch sewing machine having stitch forming means including a reciprocating needle carrying a needle thread, a thread carrying chain-stitch looper, a loop spreader allowing the forming of chain stitches in every feed direction of a workpiece, and a workpiece press pad, a throat plate, an insert received in said throat plate, said insert comprising a disk-shaped part, a stitch hole formed in said disk-shaped part, and a sectional part surrounding said stitch hole on a section of its circumference and surmounting said throat plate, said sectional part being provided with bevels extending on vertical side edges of said sectional part and having increasing widths vertically from the edge of said stitch hole to the top surface of said sectional part, for forming an enlarged supporting surface for said workpiece to prevent a downward stripping of said workpiece when pierced by said needle, and to provide as much free room as possible in the area of said stitch hole for tightening the loose needle thread loops when forming a chain-stitch scam in a relatively large area of movement of said workpiece.

2. In a two-thread chain-stitch sewing machine as claimed in claim 1, wherein said sewing machine includes a pattern controlled sewing means associated therewith including a frame, a turntable pivoted in said frame, workpiece and pattern. holders secured to the circumference of said turntable, and provided with lower and upper clamping plates and guide patterns, a link arm pivoted to said frame, a carrier arm pivoted to said link arm and carrying said sewing machine, a magnetic roller for engaging with said patterns, a magnetic roller driving shaft carrying and driving said magnetic roller, said roller shaft being arranged in said carrier arm and rotatable coaxially with the axis of said needle for driving said turntable by said roller, an elongation of said magnetic roller driving shaft beneath said carrier arm, a loose guide roller pivoted on said elongation, and an U-shaped guide rail arranged in rectilinear direction relative to the axis of rotation of said turntable and receiving said guide roller, a frustoconical section formed on said sectional part of said insert surrounding said stitch hole on a section of its circumference and surmounting said throat plate, said lower clamping plate of said workpiece and pattern holders being in alignment with said supporting surface of said insert, said lower clamping plate further provided with a bevel being so proportioned with reference to said frusto-conica] section of said sectional part of said insert as to obtain a small difference between the path of motion of said needle and the contours of said lower and upper clamping plates.

3. In a two-thread chain-stitch sewing machine as claimed in claim 1, wherein said sectional part of said insert surrounding said stitch hole is formed as a frustoconical section.

4. In a two-thread chain-stitch sewing machine as claimed in in claim 2, wherein said sectional part of said insert surrounding said stitch hole of said sewing machine is formed as a cylindrical section, and said lower clamping plate cooperating with said insert is provided with a rectangular contour.

(References on following page) References Cited UNITED STATES PATENTS Douglas 112-260 Schaaf 112-260 Wesson 112-260 XR Minehan 112-260 XR Osterhout 112-197 Barrow et a1 112-197 Becker 112-199 10 6 2,136,288 11/1938 Ebert 112-260 2,389,112 11/1945 Newton et a1 112-197 2,837,047 6/1958 Sheppard 112-260 5 MERVIN STEIN, Primary Examiner G. H. KRIZMANICH, Assistant Examiner US. Cl. X.R. 

